[Met_help] [rt.rap.ucar.edu #87446] History for why is there such values in MPR files?

[John Halley Gotway via RT]

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  Initial Request
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Hello
I wonder why there are such values in forecast columme, for instance, -2.702e-08, in some MPR files based on a same Configure file on employing point_stat tool? if it will affect the evaluation result under such conditions? Please read my attach file
I am looking forward your response. Thank you so much.
Best wishes
Sincerely
Yu Xin

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Subject: why is there such values in MPR files?
From: John Halley Gotway
Time: Fri Oct 19 12:10:44 2018

Yu Xin,

Thanks for sending the sample file to demonstrate this behavior.

These values of -2.702e-08 are very, very small slightly negative
numbers.
In practice they should have little to no effect on the actual
statistic
values you calculate since they are so close to zero.  They're most
likely
due to floating point roundoff.  I suspect if you look at the actual
values
in the input model data file, the values of 0 are stored in this way.

Since you're dealing with precip, one logical thing to do would be to
consider any value less than zero to actually be zero.  This is called
"censoring" the data in MET, and here's how you can do that in the
Point-Stat config file:

fcst =  {
   field = [
      { name = "APCP"; level = "A06"; censor_thresh = [ <0 ];
censor_val =
[ 0 ]; }
   ]
}

This tells Point-Stat that when processing the input APCP values,
replace
any precip values less than 0 with a value of 0.

Does this accomplish what you're trying to do?

Thanks,
John






On Thu, Oct 18, 2018 at 4:33 PM Yu Xin via RT <met_help at ucar.edu>
wrote:

>
> Thu Oct 18 16:33:24 2018: Request 87446 was acted upon.
> Transaction: Ticket created by learnerxy at 163.com
>        Queue: met_help
>      Subject: why is there such values in MPR files?
>        Owner: Nobody
>   Requestors: learnerxy at 163.com
>       Status: new
>  Ticket <URL:
https://rt.rap.ucar.edu/rt/Ticket/Display.html?id=87446 >
>
>
> Hello
> I wonder why there are such values in forecast columme, for
instance,
> -2.702e-08, in some MPR files based on a same Configure file on
employing
> point_stat tool? if it will affect the evaluation result under such
> conditions? Please read my attach file
> I am looking forward your response. Thank you so much.
> Best wishes
> Sincerely
> Yu Xin
>

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